Generally, a mobile unit such as a vehicle is equipped with a broadcast receiver for receiving radio and/or television broadcasting. The broadcast receiver is sometimes equipped with an information apparatus for use in mobile unit (onboard information apparatus), which detects the current position of the vehicle with a navigation system like GPS (Global Positioning System), and displays it on a display unit with a road map as the current vehicle location.
To receive a desired broadcasting station with a broadcast receiver, a user carries out tuning by manipulating the operation section such as a tuning button. The tuning operation during driving, however, is not only troublesome, but may involve danger. On the other hand, broadcast receivers are known which perform tuning using voice recognition. For example, a broadcast receiver is known which is provided with a dictionary of broadcasting station names of the whole country in advance. When a user utters a phrase common to the broadcasting station names, it searches the dictionary, recognizes a plurality of broadcasting stations, and selects a signal currently receivable at a fixed or higher level from the broadcast waves of the broadcasting stations recognized.
In addition, a broadcast receiver is known which carries out tuning using voice recognition to receive a desired broadcasting station, and which automatically creates a necessary and sufficient dictionary for the dwelling place of the user. It is equipped with a receiving channel table including words for representing receiving channels, and automatically creates a necessary and sufficient dictionary matching the dwelling place of the user to prevent the problem of the tuning position. More specifically, the broadcast receiver is provided not only with a receiving channel table including words for representing receiving channels, but also with a channel setting information storing section for storing tuning positions and receiving channels with establishing correspondence between them. When a new receiving channel is assigned to the tuning position by registering in the dictionary the word representing the receiving channel assigned to the tuning position, the broadcast receiver searches the receiving channel table for the word representing the receiving channel newly assigned to the tuning position, updates the word in the dictionary, and receives and outputs the signal of the receiving channel in accordance with the voice recognition result. Thus, the broadcast receiver automatically creates a table that assigns a plurality of abbreviations representing a broadcasting station to the receiving channel of the single broadcasting station whose broadcast area is the dwelling area of the user (see Patent Document 1, for example).
The broadcast receiver described in Patent Document 1 is a fixedly placed receiver. Thus, even if it has automatically created the necessary and sufficient dictionary matching the dwelling place of the user as described in Patent Document 1, when receivable broadcasting stations vary with the movement of the vehicle as the broadcast receiver equipped in the onboard information apparatus, the dictionary automatically created for the dwelling place of the user cannot be used.
In view of this, the onboard information apparatus dynamically changes the dictionary in accordance with the traveling of the vehicle. For example, it obtains broadcasting station names from broadcasting signals (broadcast waves) received, and updates the dictionary in accordance with the broadcasting station names. In other words, it must update the dictionary in such a manner as to add a broadcasting station name newly to the dictionary when receiving a broadcasting station not registered in the dictionary, and to deleted a broadcasting station that becomes unreceivable from the dictionary.
Patent Document 1: Japanese patent laid-open No. 2003-223183 (pp. 8-10, and FIGS. 1-9).
With the foregoing configuration, if the update of the dictionary is carried out each time the receivable broadcasting stations vary frequently depending on traveling conditions of the vehicle or receiving conditions, the conventional onboard information apparatus cannot help increasing the load on a microcomputer because of the frequent update of the dictionary. Then, if other applications (such as navigation) are executed, as is the case of the onboard information apparatus, an excessive burden is imposed on the microcomputer, offering a problem of making the operation of the onboard information apparatus unstable.
The present invention is implemented to solve the foregoing problems. Therefore it is an object of the present invention to provide a mobile unit information apparatus capable of carrying out stable operation by reducing the dictionary update frequency and the burden on the microcomputer in spite of the frequent changes of the receivable broadcasting stations.